The technical field of this disclosure is power supplies, particularly, a driver circuit for light emitting diodes (LEDs) using pulse width modulation (PWM).
Traditionally, incandescent and fluorescent illuminating devices have been used as light sources in automobiles and other vehicles. However, significant advances in the technology of light emitting diodes (LEDs) have made LEDs attractive for use in vehicles, because of their long operating life, high efficiency, and low profile.
The electrical characteristics of LEDs are such that small changes in the voltage applied to the LED lamp will cause appreciable current changes. LED light output is proportional to the LED current and, therefore, a current source is the preferred method of driving the LEDs. At present, LED drivers in vehicles use driver circuits with voltage source outputs, and current limiting resistors or linear current regulators. Current limiting resistors cause power loss, making the driver circuits inefficient. In addition, current regulation is not precise. Driving LEDs at other than nominal current can reduce LED life and produce unpredictable light output. As the application of LED""s in vehicles expands to higher power applications, such as the rear combination lights (Stop/Turn/Tail), the performance of these driver circuits is no longer acceptable in terms of efficiency and regulation.
It would be desirable to have a driver circuit for LEDs that would overcome the above disadvantages.
One aspect of the present invention provides a driver circuit for LEDs with good regulation and efficiency.
Another aspect of the present invention provides a driver circuit for LEDs maintaining operation at the LEDs"" nominal current.